This invention relates, in general, to a method of removing an adhered film from a workpiece and more particularly to a method of removing an adhered protective film from a semiconductor wafer.
In arts including the semiconductor, optics and decal arts, adhesive films, spin-on polymers and other coatings are often employed for protection and other reasons. One example of the use of a protective film occurs during the backgrind process for semiconductor wafers. Following the processing of semiconductor devices on a wafer, the wafer goes through a backgrind process where the backside of the wafer is thinned using a porous slurry or a diamond wheel. During this process, it is necessary to protect the finished semiconductor devices on the frontside of the wafer so that they are not damaged or contaminated by particulates. It is common to apply an adhesive film to the frontside of the wafer for protection of the finished devices thereon. When the backgrind process is completed, it is necessary to remove the protective film so that the devices on the wafer may be furtner prepared for packaging.
Protective tape removal machines are well known in the art. One such machine initially takes a wafer having a protective film adhered thereto from a wafer boat and transports it into a mechanical preparation tool. The mechanical preparation tool includes screws which are mechanically drawn across the edge of the protective film to peel it back from the wafer edge and initiate the delamination process. The screws create stress on the wafer which often causes microcracks to occur along grain boundaries of the wafer which may cause the wafer to break. Further, the screws often scratch the wafer and create unwanted particulates that may contaminate the device.
Once the wafer has been subjected to the mechanical preparation tool which initiates the delamination process, it is transported through a series of rollers which apply an adhesive tape to the film disposed thereon. Often, the adhesive from the tape sticks to the bottom rollers and causes the wafer to stick thereto. Even slight adhesion of the wafer to the roller causes the wafer to follow the shape of the roller (bend). This often causes cracks to occur in the wafer due to the extra stress caused by the rollers. This is especially detrimental when the wafer has previously been stressed along a grain boundary. In addition to the stress caused by the adhesive on the rollers, the rollers inherently apply additional stress to the wafer as it moves therethrough.
As the wafer moves through to the rollers, tape is applied along the entire length of the protective film. Following the application of the adhesive tape, the wafer is held in a stationary position by a vacuum chuck or the like. Once wafer is held stationary, the tape is pulled backwards at 180 degrees to the wafer surface until the protective film is completely removed. Additional stress acts upon the wafer at this point because of the tape being adhered to the film along its entire length. This often causes cracks in the wafers, especially at points where it has been previously weakened by earlier delamination steps.
Accordingly, it would be highly desirable to have a method of removing an adhered film from a workpiece that does not scratch the workpiece or cause stress to act thereupon.